Now Rasmus Nielsen of the University of California, Berkeley, and his colleagues have compared Tibetan genomes with populations from around the world. No other modern group carries the Tibetan variant of EPAS1. But they found the same gene variant in the genome of a Denisovan, an extinct species of human known only from a cave in the Altai mountains in east-central Asia (Nature, DOI&colon; 10.1038/nature13408).

“The study shows that one of the most spectacular cases of [genetic] adaptation in humans has its roots in Denisovans,” says Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

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One of the most spectacular cases of human adaptation has its roots in Denisovans

It is still unclear how the Denisovan EPAS1 gene helps Tibetans survive 4000 metres above sea level. It seems to cut the number of red blood cells, which carry oxygen, being made. That is odd&colon; most people make more of these cells when they travel to high altitudes, to carry more oxygen. But they thicken the blood, possibly making strokes more likely. Nielsen thinks that, by thinning the blood, the Tibetan gene may help lower this risk.

Denisovans are one of at least two extinct hominin species that humans mated with, the other being Neanderthals. Many of us carry bits of DNA from these other species. One Neanderthal gene found in modern Eurasians may increase the risk of type 2 diabetes.

“It is very satisfying to see that gene flow from Denisovans, an extinct group of archaic humans that we discovered only four years ago, is now found to have had important consequences for people living today,” says Pääbo.

This article appeared in print under the headline “Extinct humans primed Tibetans for the high life”